VALLEJO - About all that's left of the old Carquinez Bridge is a couple of metal towers and a section of span extending perhaps an eighth of a mile before coming to a dead end over the water.

It is a bridge to nowhere.

Slowly, ever so slowly, the 1927 cantilever bridge is coming down, and its metal parts are being shipped to the scrap heap. Demolition crews started work more than a year ago. They are to finish by year's end.

Call it reverse engineering. Today's crews are basically having to undo what the bridge builders took four years to accomplish.

"In a lot of ways, it's a tougher task to take something apart than it is to build it," said Bob Haus, a spokesman for the state Department of Transportation. "Anyone who's worked on a car knows disassembly can be even trickier than assembly."

The old cantilever bridge looked like something assembled with parts from a giant Erector set. Caltrans replaced it with the sleek, graceful Alfred Zampa suspension bridge in 2003 and began demolishing the old bridge in spring of 2006 at an announced cost of $49 million.

Blasting the bridge to pieces is no option. For one thing, the Zampa bridge carries southbound Interstate 80 traffic a stone's throw to one side. A 1958 bridge carries northbound I-80 traffic a stone's throw to the other side. Meanwhile, ships navigate the Carquinez Strait below.

So the Carquinez Bridge isn't coming down with a bang, but rather melting away a little each day.

"We're disassembling the truss member by member, which can include taking out rivets," Caltrans Engineering Technician Sean Skeen said. "But typically, we use a torch and remove the members."

Perhaps the most spectacular part of the demolition job came at the beginning. The media turned out when crews used hydraulic jacks to slowly lower the middle 700-ton bridge spans to barges waiting 150 feet in the water below.

Much of the demolition job is more mundane. Ten jacks capable of lifting up to 100 tons each are lifting the remaining bridge span a few inches off the Vallejo-side tower. Workers have already built a temporary support system underneath the span. Then they will disassemble the tower, using a crane to hoist the parts into a truck.

Finally, they will disassemble the truss until they reach land. The bridge will then be a memory, as if it never existed.

A few parts of the bridge will avoid the scrap heap and go to Vallejo and Crockett history museums, a Caltrans museum in Oakland and a vista point that Caltrans will build at the Carquinez Strait. These parts will remind people of a bridge once hailed as an engineering marvel.

"They can be as small as individual rivets," Skeen said.

And the salvaged parts can be as big as a diagonal section of the truss, some 20 to 30 feet long.

Once the bridge is down, Caltrans has one last chore to perform. It must take care of Rags.

Rags was a black-and-white mongrel that lived in Crockett, the small town on the southern side of the bridge. Rags' story is recounted in David Billeci's book "Crockett and Its People."

Workers in the mid-1950s were busy putting up the second Carquinez Bridge. Rags lived with a couple at their First Avenue house. The couple rented out their garage to a company working on the bridge.

Rags went to the bridge with the workers each day, was fed by them and returned home at night. But one day, workers closed the bridge gate on Rags without knowing the dog was still there. Rags jumped over the side of the bridge in an escape attempt and plummeted to its death.

The workers placed a stone marker in the ground beneath a pier with the words "Rags" on it as a memorial.

The Rags memorial was removed amid all the work Caltrans did on the Carquinez bridges, including the strengthening of the 1958 bridge to better survive earthquakes. The small stone marker is being kept at the Crockett Historical Society. Haus said no remains of the dog were removed.

Eventually, the Rags marker will be brought to a new landscaped area on the Crockett shore that Caltrans will put in for the bridges, Haus said. The landscaped area will be a finishing touch for the Carquinez projects.

The cantilever bridge opened with much ado on May 21, 1927. President Calvin Coolidge pressed a golden telegraph key in Washington, D.C., to start the dedication ceremony. Now, having served its purpose, the bridge is marking its 80th anniversary by disappearing.

1927 Carquinez Bridge facts-- Opened on May 21, 1927. Travelers previously had to use a ferry to cross the Carquinez Strait.-- Conceived by Vallejo grocer Aven Hanford and San Francisco grocery salesman Oscar Klatt and built as a private project.-- The bridge cost $7.8 million to construct, which is $85 million in today's dollars. California built the replacement Al Zampa Bridge for $239 million in 2003.-- An estimated 18,000 cars drove across the bridge on opening day, when the toll was waived for the occasion.-- The original toll was 60 cents, which is $6.62 in today's dollars.-- California bought the bridge in 1940.